1. Field of Invention
This invention generally relates to semiconductor manufacturing methods and, more particularly, to a method for removing organic films and materials used during semiconductor wafer fabrication.
2. Related Art
New processing and manufacturing techniques are continuously being developed to make further advancements in the development of semiconductor devices, especially semiconductor devices of decreased dimensions.
An important aspect of the semiconductor device fabrication process is the removal of the photoresist film. As the size of semiconductor devices continues to decrease, typical photoresist removal methods must be able to increase the rate of residual-free resist removal, and must decrease the amount of damage caused in the substrate layers underlying the resist film.
Typically two types of ashing methods exist—a wet method and a dry method. The wet method is generally preferable to the dry method, since it does not damage the underlying substrate. However, in wet ashing methods the chemical bath that is needed to remove the resist can also contaminate the substrate. In addition, particles that remain in the chemical bath can re-adhere to the substrate. Thus, in the wet ashing method a cleaning step is required before the substrate is ready for the anneal process.
The dry ashing method typically includes exposing the substrate and the photo resist to a plasma. The plasma formation occurs at low pressure. Thus, the amount of reactive gas available to the removal process is low. For example, in an oxygen plasma that is formed at about 1 Torr, the amount of O2 available to react with the photoresist is about 1000 times less than is available in air.
Unfortunately, substrate damage can occur as the substrate is exposed to the plasma due to the ion bombardment. In addition, dry ashing methods usually leave residue on the wafer surface even after the ashing processes are complete. As a result, the photoresist stripped wafer has to be reprocessed by wet cleaning before conducting an ion implant anneal or other process, which adds another level of complexity to the overall substrate processing.
What is needed, therefore, is an ashing method that reduces damage to the substrate, reduces the amount of residue and particle contaminates remaining on the stripped substrate and increases the throughput of the ashing process.